1. Field of the Invention
The present invention relates generally to improvements in packaging of miniaturized electronic components or the like, and more specifically to a tape carrier package having improved connecting (viz., bonding) terminals via which fine-pitch interconnections with external circuitry can effectively be achieved. Still more specifically, the present invention relates to a method of electrically interconnecting input and/or output terminals of a tape carrier package to the corresponding ones of an external component(s) or the like.
2. Description of the Related Art
As is known in the art, a tape carrier package (TCP) comprises a flexible base film-of polyimide (for example), which carries thereon a plurality of conductive leads typically made of copper and further carries one or more IC (integrated circuit) chips. The opposite ends of each of the conductive leads are coupled to connection terminals via which the TCP can be interconnected to external circuitry. Such a TCP is disclosed in U.S. Pat. No. 5,390,079 to Aomori, et al. by way of example.
Before turning to the present invention it is deemed preferable to briefly describe, with reference to FIGS. 1 and 2, a conventional technique which may be relevant to the present invention. This conventional technique is disclosed in Japanese Laid-open Patent Application No. 5-95024.
FIG. 1 is a schematic top plan view of an electronic component assembly (depicted by numeral 10) which generally comprises a TCP 12, a liquid crystal panel 14 surrounded by a liquid crystal display (LCD) terminal board 16, and a printed circuit board 18. The TCP 12 includes a non-conductive flexible base film 20 on which, in this particular case, an LCD driver IC (integrated circuit) chip 22 is mounted. The IC chip""s bonding pads are connected to the conductive leads.
As mentioned above, the TCP 12 is provided with a plurality of conductive leads on one surface thereof (the lower surface in FIG. 1 and thus the conductive leads are not shown). As shown in FIG. 1, the TCP 12 has the input side (the left side in the drawing) electrically coupled to the printed circuit board 18 using an anisotropic conductive film (ACF) 24. In a similar manner, the TCP 12 has the output side (the right side in the drawing) electrically interconnected to the LCD terminal board 16 by way of another AFC 26.
As is known in the art, an ACF is an anisotropic conductive adhesive material, and consists of conductive spheroidal particles dispersed in a thermosetting (for example) adhesive matrix. The conductive particles can typically be pure metals such as gold, silver, or nickel. Mean conductive particle sizes are about 5 xcexcm (for example).
FIG. 2 shows, in part, a cross section taken along a line Ixe2x80x94I in FIG. 1, which schematically illustrates a manner where the TCP 12 is electrically connected to the printed circuit board 18 using the ACF 24. As shown, the base film 20 of the TCP 12 has its lower surface on which a plurality of connecting terminals 27 (only three illustrated) are disposed. Each of the terminals 27 consists of an inner member 28, made of copper, which has a trapezoid-shaped cross-section and is coated (plated) with tin (Sn). In FIG. 2, the tin-coated layer is depicted by numeral 30, and the above mentioned conductive particles are indicated by numeral 32. Further, a plurality of connecting terminals on the printed circuit board 18 are depicted by numeral 34. Each of the terminals 27 is typically about 18 xcexcm high and typically plated by tin (Sn) up to a thickness of about 0.3 xcexcm. Still further, each connecting terminal 27 has a width of about 40 xcexcm and is separated from the adjacent one by about 30 xcexcm. Each of the connecting terminals 27 has a length of about 2.5 mm extending in a direction perpendicular to the paper.
When the connecting terminals 27 of the base film 20 are to be interconnected to the corresponding ones 34 of the circuit board 18, the ACF 24 is placed on the printed circuit board 18 in a manner to cover the connecting terminals 34. Subsequently, the TCP 12 is deposited on the ACF 24 after being aligned with the printed circuit board 18. Thereafter, the ACF 24 is heated and pressed with an appropriate load and then cured. Thus, the bonding terminals 27 are electrically coupled to the counterparts 34 via a monolayer of deformed conductive particles 32.
On the other hand, the interconnection of the TCP 12 to the peripheral LCD panel 16 is implemented, concurrently with the aforesaid interconnection of TCP 12 to the circuit board 18, using the ACF 26 in exactly the same manner as mentioned above.
As mentioned above, the connecting terminals 27 are electrically coupled to the terminals 34 via a monolayer of conductive particles. In such a case, an area which contributes to the actual electrical connection is as low as about 10% compared with the entire facing area of the terminals 27 and 34. If the electrically connecting area should be increased while maintaining the terminal pitch, it is necessary to elongate or extend the length of each of the connecting terminal 27 with the result of undesirable increase in the size of the LCD terminal board 16. This conflicts with the current tendency of increasing the LCD size in a very limited space. Further, in the case where the terminal pitch becomes fine, the conventional technique using the ACF may encounter the problem that a short circuit may be produced between the adjacent connecting terminals due to linkage of the conductive particles.
It is therefore an object of the present invention to provide a tape carrier package with improved connecting terminals via which the above mentioned difficulties inherent in the conventional packaging can effectively be eliminated.
Another object of the present invention is to provide a method of electrically interconnecting a tape carrier package with improved connecting terminals to an external circuit board.
These objects are fulfilled by a tape carrier package (TCP) with improved connecting terminals. The TCP includes a base film of non-conductive material which carries a plurality of conductive leads on one surface thereof. A plurality of connecting terminals are deposited on the surface such as to be electrically interconnected to the ends of the conductive leads. Each of the connecting terminals has an acute-angled top portion and comprises an inner member of a first material and an outer member of a second material plated on the inner member. The acute-angled top portion of second material is easily deformable when the connecting terminal is pressed against a corresponding terminal provided on a board to be interconnected to the TCP. Thus, an adequate interconnection area is obtained between the TCP and the circuit provided on the board.
One aspect of the present invention resides in a tape carrier package which comprises: a base film of non-conductive material, the base film carrying a plurality of conductive leads on a surface thereof; a plurality of connecting terminals which are deposited on the surface and electrically interconnected to the conductive leads, each of the connecting terminals having an acute-angled top portion and comprising an inner member of a first material secured on the surface and an outer member of a second material plated on the inner member, the second material being more readily deformable than the first material.
Another aspect of the present invention resides in a method of interconnecting a tape carrier package to an external circuit board, the tape carrier package comprising; a base film of non-conductive material, the base film carrying a plurality of conductive leads on a surface thereof; a plurality of connecting terminals being deposited on the surface and electrically interconnected to the conductive leads, each of the connecting terminals having an acute-angled top portion and comprising an inner member of a first material secured on the surface and an outer member of a second material covering the inner member, the second material being more readily deformable than the first material, the method comprising the steps of: coating an adhesive on an area including a plurality of connecting terminals which are deposited on the external circuit board and which are made of material similar to the first material; placing the tape carrier package on the external circuit board in a manner where the connecting terminals of the tape carrier package are aligned with corresponding connecting terminals of the external circuit board; and pressing the tape carrier package towards the external circuit board such that the acute-angled top portion contacts a corresponding connecting terminal of the external circuit board and establishes a pressure-contact therewith by elastically deforming the acute-angle top portion.